The invention relates to test apparatus for optoelectronically evaluating test paper strips such as are used for determining blood sugar levels, comprising a case having a battery compartment and means for holding the test paper strip, a light source illuminating the test paper strip, a photosensor receiving the light reflected from the test paper strip, and calibratable electronic evaluation and display means receiving and controlled by the photosensor output.
The invention relates to an improvement of the optoelectronic test device-including the light source and the photosensor-in regard to the dark-calibration of the test apparatus.
The known devices of the type specified above must be calibrated before each use, requiring a so-called light-calibration, which is performed on the untreated, i.e. not yet discolored test paper strip, and a so-called dark-calibration, which is performed on a separate black calibrating strip. Apart from the fact that the necessity of performing a dark-calibration each time the device is put into use is far from user-friendly, dark-calibration by means of the black calibrating strip is not too accurate because the absorptive properties of the black calibrating strip may change after repeated use due to dirt, skin grease and finger stains or prints.
Also, this type of test apparatus is used in connection with test paper strips which have a chemically active section. The producers of these strips do in fact try to make them as uniform as possible in quality. Still, it cannot be avoided that the reaction properties turn out to differ substantially between production batches.
In the case of test paper strips for determining blood sugar levels, one and the same blood sugar content may in fact cause test paper strips of one batch to become darker than test paper strips from another batch. In the past, this uncertainty had to be accepted although it constituted a substantial disadvantage.